Engineering topics
Publications and source records attributed to Lal, R. B..
Holographic flow field analysis has been applied in a crystal growth experiment conducted on NASA's space shuttle program on Spacelab-3 during April 29 - May 6,l985. The experimental holograms taken during the crystal growth process are reconstructed into interferograms and later digitized to give refractive-index fields: A comparison has been made with theoretically computed interferograms.
The cooled sting technique used to grow triglycine sulphate (TGS) crystals is investigated. The sting procedure, which achieves supersaturation by cooling the seed crystal mounted on the sting is described and a diagram is provided. Temperature differentials of 1.5 and 1.0 C are optimum for growing (001) and (010) orientation TGS seeds. The data obtained are compared with previous data and good correlation is shown; it is inferred that TGS crystals of any orientation can be grown at a uniform rate of 1 mm/day using this technique.
In a low-g environment, buoyancy driven convection effects in solution crystal growth are greatly reduced and, thus, one can study diffusion mass transport which in 1-g is masked by convective phenomena. Crystals of triglycine sulfate (TGS) will be grown aboard the Spacelab 3 mission, using a specially developed Fluids Experiments System (FES). The objectives of the experiment are: (1) to develop a technique for solution crystal growth in a low-g environment, (2) to characterize the growth environment provided by an orbiting spacecraft and to determine the influence of the environment on the growth behavior, and (3) to determine how gravity in a low-gravity environment influences the properties of a resulting TGS crystal. Single crystals of TGS have been grown using conventional low-temperature solution crystal growth method and the growth process has been extensively characterized. Various physical properties of TGS solution have been measured. Also, a unique technique of growing solution growth crystals by extracting heat at a programmed rate from the crystal through a semi-insulating sting has been developed and tested in 1-g environment.
Automatic crystallizer grows crystals from aqueous solutions. Crystals grown from aqueous solutions by slow cooling of growth solution along with forced convection to increase mass transfer.
Experimental system for monitoring growth of triglycine sulfate (TGS) crystals from solution is being studied. System consists of outer cell containing distilled water heated and stirred to maintain constant temperature to within plus or minus 0.1 degrees C, inner (growth) cell containing supersaturated solution of TGS, and seed crystal mounted in plastic-covered stainless-steel sting equiped with controlled cooling mechanism and temperature sensors.
The growth of crystals from solution is greatly influenced by buoyancy driven convection. In a low-g environment, convection is greatly suppressed and diffusion becomes the predominant mechanism for thermal and mass transport. An experiment to grow TGS crystals by solution technique during the orbital Spacelab III mission has been designed. Crystals are grown by a new and unique technique of extracting heat from the crystal through a sting. The cooling at the sting tip is responsible for the desired supersaturation near the growing crystal. Calculations indicate that the cooled sting technique for solution crystal growth is necessary in low-g to maintain a maximum growth rate of 1 mm/day. Results of groundbased work in support of the flight experiment are discussed.
The mechanism of crystal growth by solution technique was studied. A low temperature solution crystal growth setup was developed. Crystals of triglycine sulfate (TGS) were grown using this arrangement. Some additional tasks were performed toward fabrication of experiments for future space flight.
The advantages and mechanisms of crystal growth from solution are discussed as well as the effects of impurity adsorption on the kinetics of crystal growth. Uncertainities regarding crystal growth in a low gravity environment are examined. Single crystals of triglycine sulfate were grown using a low temperature solution technique. Small components were assembled and fabricated for future space flights. A space processing experiment proposal accepted by NASA for the Spacelab-3 mission is included.
The mechanism of crystal growth was studied by solution technique and how it was affected by space environment. Investigation was made as to how space processing methods are used to improve the promising candidate materials for different devices.
A study was undertaken to analyze different growth techniques affected by a space environment. Literature on crystal growth from melt, vapor phase and float zone was reviewed and the physical phenomena important for crystal growth in zero-gravity environment was analyzed. Recommendations for potential areas of crystal growth feasible for space missions are presented and a bibliography of articles in the area of crystal growth in general is listed.
Materials were selected for device applications and their commercial use. Experimental arrangements were also made for electrical characterization of single crystals using electrical resistivity and Hall effect measurements. The experimental set-up was tested with some standard samples.
A handbook is presented of materials feasible for growth in space in future NASA Missions. Major emphasis was placed on a literature survey concerned with promising materials. Equipment for resistivity and hall effect set-up was procured.
Theoretical and experimental work reported relates to the effects of near-zero gravity on growths of crystals and metallic whiskers during Skylab and Apollo flight experiments. Studies on growth and characterization of candidate materials for flight experiments cover indium-bismuth compounds, bismuth single crystals, gallium arsenide films and single crystals, and cadmium whiskers.
In-Bi whisker growth by squeeze technique, measuring crystal structure by X ray analysis and melting point method
Electron paramagnetic resonance of photosensitive donors in zinc oxide with oxygen vacancies
UV irradiation effect on electrical conductivity of zinc oxide single crystals